'Solar flow battery' combines storage with efficiency

October 01, 2018 // By Nick Flaherty
Researchers in the US and Saudi Arabia have combined a solar cell and battery in one device to create a "solar flow battery" that is more efficient that the separate systems.

"Compared with separated solar energy conversion and electrochemical energy storage devices, combining the functions of separated devices into a single, integrated device could be a more efficient, scalable, compact, and cost-effective approach to utilizing solar energy," said Song Jin, a professor of chemistry at the University of Wisconsin-Madison. Jin and his team developed the device in collaboration with Jr-Hau He, a professor of electrical engineering at King Abdullah University of Science and Technology (KAUST).

The solar flow battery (SFB) developed by the team has an efficiency of 14.1%, using high-efficiency 2.4V tandem III-V photoelectrodes that are  matched with high-cell-voltage redox flow batteries and carefully designed flow field architecture. The low cost organic redox materials are 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-OH-TEMPO) and methyl viologen (MV) as the anolyte and the catholyte.

The SFB has three different modes. If energy is needed right away, it acts as a solar cell and immediately converts sunlight to electricity. Otherwise, the device can soak up solar energy by day and store it as chemical energy to deliver it later as electricity when night falls or the sky grows cloudy.

The device can also be charged by electrical energy if needed, just like a typical battery. The team's most recent solar flow battery model is able to store and deliver electricity from solar energy more efficiently than any other integrated device.

"These integrated solar flow batteries will be especially suitable as distributed and stand-alone solar energy conversion and storage systems in remote locations and enable practical off-grid electrification," said Jin.

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